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X80 pipeline steel has played a vital role in oil and gas transportation in recent years. However, hydrogen-related issues frequently lead to pipeline failures during service, resulting in significant losses of properties and lives. Three heat treatment processes (furnace cooling (FC), air cooling (AC), and water cooling (WC)) were carried out to investigate the effect of different microstructures on hydrogen-induced cracking (HIC) susceptibility of X80 pipeline steel. The WC sample demonstrated the highest hydrogen embrittlement index, registering at 21.9%, while the AC and FC samples exhibited progressively lower values of 15.45% and 10.98%, respectively. Under equivalent hydrogen charging durations, crack dimensions with a maximum length exceeding 30 μm in the WC sample generally exceed those in the FC sample and AC sample. The variation is attributed to the difference in microstructures of the samples, predominantly lath bainite (LB) in water-cooled samples, granular bainite (GB) in air-cooled samples, and ferrite/pearlite (F/P) in FC samples. The research results demonstrate that the sensitivity of lath bainite (LB) to HIC is significantly higher than that of pearlite, ferrite, and granular bainite (GB). The presence of a large amount of martensite/austenite (M/A) constituents within bainite results in a multitude of hydrogen trap sites. HIC cracks in bainite generally propagate along the profiles of M/A constituents, showing both intergranular and transgranular cracking modes. [ABSTRACT FROM AUTHOR]

The purpose of this work is to study the effect of charging conditions on hydrogen damage. The effects of electrochemical hydrogen charging current density and time on hydrogen-induced blistering (HIB), cracking behavior, and mechanical properties of Q690 steel are studied by electrochemical hydrogen charging, microstructure observation, and slow strain rate tensile (SSRT) tests. The results show that HIB and internal cracks occur when the Q690 steel is charged at different current densities. The charging conditions have a significant effect on the HIB characteristics of the material and the morphology, number, size, and location of internal cracks. The geometrical parameters of blisters on the surface of Q690 steel are quantitatively evaluated, and deeper cracks are found at higher hydrogen concentrations. At high hydrogen charging current density (50 mA/cm2), due to the accumulation of a large number of hydrogen atoms and the precipitation of hydrogen, the active sites on Q690 steel surface increase dramatically, leading to the initiation of a large number of blisters. At this time, high current density is responsible for the initiation of blisters. The relationship between hydrogen charging current density and mechanical properties of Q690 steel is studied, and the change in the fracture morphology is observed. The Q690 steel was damaged and failed due to an internal crack caused by excessive hydrogen pressure. On the other hand, electrochemical hydrogen charging leads to the degradation of mechanical properties and the transition from ductile fracture to brittle fracture. [ABSTRACT FROM AUTHOR]

Water-based lubrication faces the common challenge of component lifetime extension which is impaired by tribocorrosion due to material surface depassivation. However, such mechanisms in a pH-neutral and low-halide electrolyte require additional understanding. A ball-on-flat configuration study of hard-phase materials in a low amplitude–high frequency sliding contact against martensitic chromium steel with contact pressures around 200 MPa is presented. Under lubrication by purified water, tungsten carbide-based metal matrix composite (MMC) with NiCr binder and silicon nitride-based ceramic (SiAlON) against DIN/EN 1.4108 steel yielded coefficients of friction above unity. Wear scar enlargement led to fretting-like conditions with adhesion becoming the fundamental wear mechanism. A tribocorrosion-induced depletion of tungsten carbide and nickel was determined for MMC. SiAlON materials suffered extreme wear under the formation of abrasive SiO2, while heat-treated DIN/EN 1.4125 steel showed lower friction and wear, but also showed signs of hydrogen embrittlement. Results from accompanying single-material corrosion experiments could not satisfactorily explain the phenomena. Including galvanic interaction and the influence of contact geometry, a new tribocorrosion model for fretting conditions is proposed. It describes an expanding anodic belt located at the inner-most crevice position of an otherwise cathodically polarized material. Low conductivity of the electrolyte is seen as a key player in this process, while the galvanic situation between two materials in contact was shown to invert when water was substituted by a wet organic phase. [ABSTRACT FROM AUTHOR]

• Develop a phase field method for assessing the threshold conditions to initiate hydrogen-induced cracks on dented pipelines. • Define the influences of dent depth, initial hydrogen concentration and internal pressure on crack initiation. • Determine the threshold values of dent depth and internal pressure to initiate cracks under hydrogen impact. An accurate determination of the threshold conditions to initiate cracks on aged hydrogen pipelines is paramount for ensuring energy transport safety. In this work, a finite element-based phase field method was developed to assess the crack initiation on dented pipelines while considering the hydrogen (H) impact. Theoretical and multi-physics numerical formulas were derived for prediction of the elastic-plastic fracture behavior of H-contained steel. A critical phase field parameter, ϕ =0.69, is defined for predicting crack initiation at the dent on pipelines. The presence of H within the steel decreases the threshold dent depth for initiating H-induced cracks. When the initial H concentration increases from 0 to 0.5 wppm, the maximum dent depth for crack initiation reduces from 17.5 mm to 10.7 mm. The maximum dent depth required for crack initiation reduces from 17.5 mm to 7.8 mm when an internal pressure of 8 MPa is applied on the steel pipe. The site with the maximum phase field parameter changes during indentation, implying that the location initiating cracks depends on the dent dimension. The existing criteria in ASME B31.12 standard are not applicable for predicting H-induced crack initiation on dented pipelines. This study proposes a new method to predict hydrogen-induced cracking on aged pipelines when transporting hydrogen. [Display omitted] [ABSTRACT FROM AUTHOR]

• HIC API 5L X65 steel was investigated. • Stress relieving was carried out at different temperatures. • HIC resistance of was investigated in NACE solution A. • HIC susceptibility and inclusion relationship was investigated. • Improved HIC resisatnce was linked with the reduction in residual stresses. This study investigates the hydrogen-induced cracking (HIC) of a thermomechanical controlled processed (TMCP) API 5L X65 steel pipe fabricated using the JCOE forming process. Despite passing HIC testing as a plate, the final pipe exhibited unexpected failure, highlighting the critical influence of pipe fabrication on material performance. In this study, failed pipes were subjected to heat treatment, and HIC testing following NACE TM 0284 standard, SEM, and EDX examinations. The effect of heat treatment on the grain size, residual stress and susceptibility to HIC was investigated. The findings revealed that welding played a detrimental role, as all the HIC failures occurred at the welded area (0° orientation) due to welding-induced stresses and potential microstructural changes. It is believed that the welding process imposed reversible hydrogen traps in the HIC resistance plate ultimately reducing the HIC resistance. The heat treatment proved an effective method for relieving the applied micro-residual stresses that resulted in enhanced HIC resistance of the material. [ABSTRACT FROM AUTHOR]

• Modifying microstructure influences hydrogen diffusion and cracking of steels. • HIC susceptibility of steels is dependent on their diffusion characteristics. • Phase composition was seen to play the most significant role in influencing HIC. • Low local misorientaions in steels facilitates the elimination of HIC. This work examines the effect of stress-relief (SR) and quenching and tempering (QT) heat treatments on the hydrogen-induced cracking (HIC) susceptibility of pipeline steels. Two trials of a similar X65 pipeline steel were used in this study. They had distinct differences in microstructural characteristics, which significantly affected their cracking behaviour. The SR treatment reduced local misorientations, without significantly altering the microstructural appearance of the steels. Hence, this treatment resulted in a hydrogen permeation transient and cracking response similar to the as-received steels. However, the QT treatments significantly modified the microstructure of the steels, with some treatments resulting in equiaxed polygonal ferrite grains and lower local misorientations, depending on the quenchant used. These microstructural changes contributed to increasing hydrogen diffusion and permeation through the steels, as well as alleviating or eliminating HIC after hydrogen charging. Comparing the permeation transients and diffusion characteristics of the steels without cracks to those with significant cracking, a dependence of HIC susceptibility on the diffusion and trapping behavior within the steels was observed. [ABSTRACT FROM AUTHOR]

We investigate the corrosion-electrochemical properties of 17G1SU steel in chloride-acetate solutions for different concentrations of hydrogen sulfide. It is shown that, if this concentration increases, then the corrosion potential of steel shifts to the side of more negative values and the corrosion rate increases almost linearly. The presence of hydrogen sulfide does not affect the values of Tafel constants of the cathodic and anodic reactions. It is shown that the rate of cathodic reactions may become higher as a result of the direct reduction of hydrogen from H2S molecules. For hydrogen-sulfide concentrations > 1500 mg/dm3, the rate of cathodic processes decreases due to the complications of diffusion, which may be caused by the adsorption of hydrogen-sulfide molecules and a decrease in the rate of catalytic recombination of adsorbed hydrogen atoms. Hydrogen-induced cracking of stress-free steel is revealed for hydrogen-sulfide concentrations ≥ 500 mg/dm3. [ABSTRACT FROM AUTHOR]

Hydrogen diffusivity and trapping have been studied in two advanced high strength steel grades and model samples using electrochemical permeation test. Microstructures of CP1000 and DP1000 steels consist of ferrite, martensite and a small fraction of retained austenite. In addition, bainite is present in CP1000. Model phases with predominance of a particular phase have been prepared by specific heat treatment. DP1000 has shown the lowest diffusivity among all materials, while ferritic model sample has shown the highest. Differences in hydrogen diffusion coefficient values are linked to trapping microstructural characteristics and grain size. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) and hydrogen-induced cracking (HIC) behaviour of a X65 steel pipeline weldment were investigated using slow strain rate tensile (SSRT) testing of specimens that were specifically extracted from different zones of the weldment (i.e., weld metal (WM), heat-affected zone (HAZ), and base metal (BM)). The WM was found to be the most susceptible zone to HE and HIC, while BM the least. Analysis of microstructure, fracture surface, secondary crack formation, and mechanical behaviour revealed that the high HE susceptibility of WM is correlated to microstructural features including Ti-rich inclusions, martensite/austenite (M/A) constituents, and prior austenite grain boundaries (PAGBs). • Susceptibility of a pipeline steel weldment to HE and HIC was assessed and discussed. • Specimens from each zone of the weldment were hydrogen charged for SSRT test. • The weld metal was found to be the most susceptible zone to HE and HIC. • HE susceptibility of the weld metal is correlated to several microstructural features. • HIC was found to initiate from Ti-rich inclusions, M/A constituents, and PAGBs. [ABSTRACT FROM AUTHOR]

The factors affecting hydrogen trapping at the non-metallic inclusions (NMIs) are identified by a combined experimental and theoretical study. The calculated results based on the proposed models show that the hydrogen trapping capacities at the NMIs decrease in the order of E b TiC > E b TiN > E b Al 2 O 3 > E b FeO > E b MnS . The interfacial sinking of hydrogen leads to the formation of a silver particle-denuded zone around the NMIs. The elastic property of NMIs is more important for hydrogen trapping than the misfit strain. This work unveils the hydrogen trapping-dependent mechanism on the composition, the misfit strain, the elastic properties, the shape and the size of NMIs. • Theoretical models are built to calculate hydrogen trapping at the inclusions. • Hydrogen distribution around the inclusions is experimentally observed. • The hydrogen trapping capacities of the inclusions are theoretically calculated. • The experimental results are explained using the proposed theoretical models. • The key factors that affect hydrogen trapping at inclusions are determined. [ABSTRACT FROM AUTHOR]

We determine the mechanical properties of the base metal and the metal of the heat-affected zone for welded joints of 17G1SU pipe steel in air and establish the influence of corrosion defects in these zones after preliminary holding in a NACE solution of hydrogen sulfide for 200 h. It is shown that the hydrogen-sulfide medium insignificantly changes the strength (σ, σ) but noticeably affects the plasticity (ψ, δ) both of the base metal and of the weld metal. We also investigate their corrosion resistance, susceptibility to hydrogen-induced cracking, and the influence of preliminary hydrogen-sulfide corrosion on the corrosion-cracking resistance of welded joints. [ABSTRACT FROM AUTHOR]

Corrosion and corrosion-mechanical properties of 35KhF low-alloyed steel in hydrogen-sulfide media are investigated. The corrosion resistance and resistance to hydrogen-induced cracking of the steel of different heats in NACE solution and artificial seawater, and its resistance to hydrogen-sulfide stress corrosion cracking in the NACE solution are determined. It is shown that 35KhF steel can be used for the manufacture of critical components of a lift string for pumping-over stratal water. [ABSTRACT FROM AUTHOR]

The spatial distribution of plastic deformation and grain orientation surrounding hydrogen-induced cracks (HIC) is investigated in samples of API-5L-X46 pipeline steel using scanning electron microscopy and electron backscattering diffraction (EBSD). This work shows direct experimental evidence of the influence of microstructure, microtexture and mesotexture on HIC crack path. [Copyright &y& Elsevier]

• The ratio of crack depth/length increases with hydrogen concentration. • Variance of internal pressure responsible for the different crack structures. • Crack geometry parameter defined as a useful indicator of internal pressure. Quantitative prediction of the hydrogen-induced crack initiation remains challenging, partially due to the difficulties in directly measuring the hydrogen gas pressure in the crack cavity. Through detailed cross-sectional observations, this study shows that the structure of the internal cracks beneath the surface blisters, i.e., the ratio of crack depth/length, can be significantly influenced by the hydrogen charging conditions. This is attributed to the change of hydrogen gas pressure in the crack cavity at different hydrogen contents, supported by the formation of stepwise cracks near the specimen surface as well as the hydrogen concentration measurements. The post-failure crack geometry is considered a useful indicator of the level of internal gas pressure to quantitatively assess the hydrogen-induced cracking sensitivity. The mechanisms of crack initiation and propagation at different hydrogen concentrations are discussed. [ABSTRACT FROM AUTHOR]

Three grades of high strength pipeline steel (API X60, X60SS, and X70) are subjected to cathodic hydrogen charging to determine the susceptibility of each steel grade to hydrogen‐induced cracking (HIC). The specimens are subjected to tensile stress until failure to generate stress‐strain, ductility, and toughness data. The fractured specimens are analyzed using a scanning electron microscope equipped with an EDS detector to determine crack initiation sites for the investigated grades of steel. The expectation that the X60SS steel grade will perform better than other grades is not met, instead it is found that under the cathodic hydrogen charging condition, the X60SS is more susceptible than the other two steel grades with respect to loss of toughness, ductility, and ultimate tensile strength. The presence of Ca‐Al‐based inclusions is the most common along the fracture surfaces. Therefore, these inclusions also act as fairly strong trapping sites that under plastically strained conditions, they can result in fisheye features which severely impact the mechanical properties of the steel specimens. [ABSTRACT FROM AUTHOR]